High-power microwave technology, too has similar potential, but has not been funded as generously as high-energy laser weapon development programmes. LIPC has significant potential especially as a non-lethal weapon. PBWs at this time are apt to remain in the science fiction domain, as the weight and cost as yet do not justify achievable military effect.
Though technology needed for PBWs exists and seems feasible, it is too impractical for miniaturisation and operational deployment. There are no known operational PBWs and, as of now, such weapons exist only in science fiction and artists’ imagination (Figs 3 and 4). Fig. 5 shows yet another PBW called Disruptor known in science fiction.
A PBW is a form of directed energy weapons (DEW that uses atomic or subatomic particles accelerated to the speed of light or near speed of light with the help of powerful electric and magnetic fields in a particle accelerator. The particles are directed to deliver a fraction of their kinetic energy to the intended target, thereby causing severe damage due to disruption of its atomic structure. It is characterised by beam energy in electron-volts, beam current in amperes and beam power in watts.
PBWs come in two primary types: charged-particle weapons and neutral-particle weapons. When it comes to military application of these different types of PBWs, charged-particle weapons are endo-atmospheric, while neutral-particle weapons are exo-atmospheric.
At the core of a PBW is the particle accelerator. It is also the most complex part of the beam weapon and is built using a linear electric field to accelerate charged particles similar to Gauss or coil gun or an induction linear accelerator system.
Induction linear accelerator consists of a simple non-resonant structure where drive voltage is applied to an axially symmetric gap that encloses a toroidal ferromagnetic material. Change in flux in the magnetic core induces an axial electric field that provides particle acceleration.
A particle beam consists of protons, electrons or neutral atoms flowing with real or imaginary current. It is characterised by beam energy, current and power. Beam energy is expressed in mega electron-volts (MeV). One eV is the kinetic energy of an electron that has been accelerated by an electric potential of one volt. Particle beam energy is characterised by the energy of a typical particle of the beam as all particles in a beam will have been accelerated to the same velocity. A PBW capable of inflicting serious damage to a target 1000km away in space would typically require beam energy of 1GeV.
An estimate of the number of charged particles in the beam can be made from the magnitude of beam current. It is possible to assign a current to the particle beam, assuming that each particle has a charge quantum equal to that of an electron even if the charged particle was the neutral atom. Beam current for the possible beam weapon described above would typically be 1000 amperes.
Power of a particle beam is the rate at which beam energy is transported, which is also indicative of the rate at which it can deposit energy into a target. As an analogy to electric circuits, the particle beam in watts is equal to the product of energy in electron-volts and the beam current in amperes.
Types of PBWs
There are two broad categories of PBWs, namely, charged-particle beam (CPB) and neutral-particle beam (NPB) weapons. CPB weapons have a set of technological characteristics that are entirely different from NPB weapons. While characteristics of the former make these suitable for use within the atmosphere, the latter are better suited for use in space.
Both endo-atmospheric (used within atmosphere) and exo-atmospheric (used in space) beam weapons have their own technological hurdles to overcome. A particle beam propagating through atmosphere requires having extremely-high power and precisely-defined beam characteristics.
Technologies required for the development of a suitable power supply and particle accelerators with sufficient power and appropriately-shaped pulses for endo-atmospheric weapons are very complex and involve high risk.
On the other hand, the greatest challenge in the case of exo-atmospheric beam weapons is in the area of beam control. The PBW should not only be able to produce a high-intensity low-divergence particle beam at the exit of the accelerator, it should also have the necessary beam-control mechanism for aiming and beaming at the target, and the ability to detect pointing errors in the beam for applying correction, if required.
Because of these two different sets of demands, endo- and exo-atmospheric devices represent two different types of weapon systems in appearance and operation. Nevertheless, there are certain fundamental areas of development that are common to both types of PBWs.
Charged PBWs. A CPB consists of electrons accelerated to the required energy level in a particle accelerator using a combination of electric and magnetic fields. To be able to destroy the target, particle energy should be high, and so should be the beam current. As an example, a practical electron beam weapon would need to hit a target 1000km away with a 1000-ampere beam with energy of 1GeV for 0.1 millisecond to destroy it.
Particles in the beam have kinetic energies equal to their rest-mass energies, with the result that these would travel with nearly the speed of light. Particle accelerators researched for high-energy physics have high energies and pulsing rates but low beam currents.
On the other hand, particle accelerators related to fusion research generate high beam currents but at low energies and pulsing rates. Particle accelerators suitable for producing beam weapons need to generate high-intensity and high-energy particle beams.
CPBs are of little use in space. The combined effects of emittance and Coulomb’s force of repulsion between like-charged particles broaden the beam. As an example, a 1GeV, 1000-ampere CPB would spread from 1cm to 5m over 1000 km.
Further, the beam is deflected by Earth’s magnetic field. By the same study, the 1GeV, 1000-ampere beam would deflect by 1000km over 1000km distance due to Earth’s magnetic field. CPBs though can be made to propagate satisfactorily over a few kilometres through an air channel evacuated by heating air in a straight line. Thus, a CPB weapon could be employed for ballistic missile defence. The system could be installed in a few ground based sites in conjunction with either Earth-borne or space-borne radar systems to identify and track incoming ballistic missile warheads.
The CPB weapon could be rapidly pointed at the incoming missile to destroy it. For an interception in air at 10km, an electron beam weapon would typically require 500MeV beam energy and 10,000 amperes of beam current. However, large fixed installations required for CPB weapons, as per current status of technology, may render these vulnerable to sabotage or other forms of attack by an adversary.
Neutral PBWs. A NPB weapon consists of neutral atomic particles accelerated to a high kinetic energy level in a particle accelerator. The process of generation of high-energy NPB is as follows:
Hydrogen or deuterium gas is subjected to an enormous electrical charge. The electrical charge produces negatively-charged ions that are accelerated through a long vacuum tunnel by an electrical potential in the hundreds-of-megavolt range. After the negatively-charged ions have been accelerated, at the end of the tunnel, electrons are stripped from the negative ions, thereby forming the high-speed NPB.
Weapons-class NPB weapons also require energies in hundreds of MeV and beam powers in tens of megawatts. Modern devices have not yet reached this level. Given the state of the art in accelerator technology, achieving the required beam energy and power levels would require hundreds of tons of accelerator hardware and enormous power sources to operate. Due to size, weight, power constraints and inherent complexity, it does not appear feasible that a NPB weapon would see the light of the day before 2025.
NPBs travel in a straight line once these have been accelerated and magnetically pointed just before neutralisation in the accelerator.
Also, an NPB is strongly affected by passage through the atmosphere. It gets attenuated and diffused as it passes through dense gas or suspended aerosols, which makes it far more suitable as compared to a CPB for applications in space against high-flying airborne or space borne targets.
Damage assessment of the target could be possible. When the beam penetrates a target, the target’s atomic and subatomic structure produce characteristic emissions that could be used to determine the target’s mass or assess the extent of damage to the target.
The major disadvantage of a NPB weapon even in space is that it is extremely difficult to sense, which complicates the problem of beam control and direction.
In the next part, we will learn more about PBWs. In subsequent parts, we will look at high-power microwaves, less-lethal weapons and high-energy laser weapons.
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Dr Anil Kumar Maini is former director, Laser Science and Technology Centre, a premier laser and optoelectronics research and development laboratory of Defence Research and Development Organisation of Ministry of Defence